Method of removing oxygen from titanium metal



Uni cdst te P fi No Drawing. Application November 8, 1955 a e Serial;No.545,7 9li 6 Claims. (Cl. 14813.1)

i This invention fre'lates toapr'ocejssfo'r removing oxygen asga, contaminant from 'titaniumifcontaining material such as'metallic titanium scrap of. titanium alloy scrap. More particularly, it relateslto a'proce'ss' in which oxygen containing metallic, titanium or titanium alloys is reacted with oneorfl mo're alkali metal fluotitanatesrin which Tthe the presenee of carbon; The/Products, of the reaction include a titanium metal product in which 'the oxygen content is substantially lower than that originally, present therein, one ormore complex alkali metal titaniumiifio' rides'inwhich the titanium hasa valence of, at least two and less than four and one or more gaseous materials fro'rnjthe ,group consisting. of, carbon monoxide,v carbon dioxide and oxygenff l Various expedients have bced'suggested in the past for the, removal of oxygen irom titanium. Because of the tenacity withfjwhich oxyg e'n is held in combination, ma t r thesesuggestionshaveinvolved melting the oxy g'eiifcontaminated titanium and r'eactionofthe oxygen with apowe'rfulreducing agentsuch as'a'n alkali metal or alkaline earth fmetal or'jwith' carb on under a high vacuum. JSnch. suggestions require, expensive reagents and, complicated apparatus resistant to attackfby' molten titanium. l

In'a copendin'g' application, Serial No, 45 5,068Q'filed September 9, 1954, by Merl e E. Sibert and Quentin HI McKeimag' nowgUnited States Patent Number 2,7 ,182, there are disclosed similar j reactions involving the various 6 "des oftitaniumflcarbonand the alkali metalfiuotitanates hichfthetitanium istetravalent.I p H A 'thatthe'teehni'ques therein dis 1', 'n u metai m alloys, whereby theremo'val" of substantial 'of oxygen may be"efiected attemperamres'well belbv'g'the lting'point ofjthe metal or alloy and whereby lowe'r 'valentalides' may'alobejobtainedas a valuable pr'odii'cfo'f' the reactionf' 1.1. V -*Inaccordancejwi h myf inventionthe oxygen content of; anii'riat'ed-met allicti anium'for titanium alloys may lie-"substantially diminished "and even entirely removed by simple thermal reaction hetween theconta mi-i ali;-me'tal'fiuotitanate, in

e p alence from; In'my process the' 'iinpure metallic 'nia ri'alfi's irnmersedin a fused salt melt 'c'iiin'sistin'gfof one w ere alkali lIl al fluotitanat'es preferably niaintained under an aands pere which is inert with i'e'spec't to {the -reac'tants'. The reaction is carried 1 the presence of carbon,- provided in any convenient as pell'ets o'r as powder distributed throughout thei= 'ras the vessel-' cont'ainin'g'the, fused melt I prefer toroperate; at a tempera'ture between 780 C. and about l 150 CF' I desirable to'i n'cludeone or more alkalimetal' -'chlor ides, iie. sodium; potassium or lithium chloride, in the rea'ction'mixtureas a'diluent salt. As a result of the'i reaction",;o ne or more alkali; metal-titanium double ffluoridesin -which '-the titanium has a valence ofle's's than fou'r-i's p'r'oducedauc'l the*oiiygen- "content of the' titanium istetravalent, thereactionlbeing carried out in tures to evolve tetra-bromides and tetra-iodides of-titanimbt 9 2,844,499 Patented July 22, 1958 carbonin the'sys te'm. The alkali metal-titaniumdouble 5 fluoride product of the reaction 'mayhe recovered from the reaction residue either before'or after'the purified solid metallic material and-lany other solidslpresent have been removed. The lower, va'le'rit product is separated either; by.- aqueous separationtechniques or" in the form of "a.

molten bath'of the product salt. I a

the invention include sodium fluotitanate', potassium'fluoj-l titanat'and lithium fluotitanate. In order. to avoid unf' desirable side reactions and, possible contaminatioriof the product, the fluotitan'ate employed should be of recrystal lized quality." That is to say thefiiiotitanate shouldbe' substantially free of -silica andfime'tallic impurities and should, contain" less than'abofitIL01-% Water and.01%. insolubles. Because of the'relative cheapness and avail-1 ability" of potassium fluotita'nate, 1 presentlylpreferto use, this ifluotitanatein the process. Therefore, in the interest; of, simplicity, the invention will be. described in connection with thefuse of potassium fluotitanateas 'a representative} formation of titanium oxy fliiorides. Bromideandiodide's' of-the alkali metals do not dissolve titanium oxides but these halides form unstable titanium bromides and iodides which decompose or;v disproportionate at high tempera- The metallictitaniumto. be purified is in any form having a large surface area.to weight ratio.,,Preferably, it is' in the formofj owder'; turnjfi sefi pings, shavin s, orsmall pieces oflight igage platej'rather than vin the. form; ofybulky pieces of considerabl thickness. I is con ventionalin the processing of .sjuch scrap, any extraneous, coatings'should be removed from thejscrap andjorga'nid residues should alsobe'rfemoved, for 'e'xample by. degreasE,

ing with trichloroethylenei iThep'jrocessed scrap freed from dirt and other "grossimpurities is next reduced to small 'pieces by chopping, shredding, or others'uitable' procedur preparatory to, charging samejintofthe' reaction mixture. f w". b 1 1} The carbon'employed should also lie-very pure: is preferably I very finely; divided in order. that it may. be readily dispersed throughout thereaction .mixtur'ef A suitablef'so'urce of carbon is lampblack which has been calcined "at a temperature of atfleast; 1500". C. in'a high vacuum prior .to addingit to thejreaction mixture; f

j The proportions of the severaliiigredient's are not criti-. cal, but j'I have founditdesirable for, the amountl"of carbon present to exceed the amount of oxygen-contained in'the mixture} Because ofjthe difficult'y inherent in .bring ing the carbon and the oxygen contaminated metallic portion'of the ch arge into intimate contact, I prefer. to provide atlfiast about2 /2 atomsof carbon for each atomj of oxygen'in the mixture. Underthe conditions of the.

processlfthe severalingredients interact to-producelcom plex potassium and titanium fluorides inwhich the titanium as ay nc les t a i ur and orem Que n-f om themetal; .l

flThe .alkali'metal fluotitanates useful inthe'practice The reaction between the oxygen contaminated metal, carbon and potassium fluotitanate is carried out by bringing the metal and carbon into contact with potassium fluotitanate in an atmosphere inert with respect to the reactants at a temperature above the melting point of the fluotitanate but below that at which the resulting lower valent complex titanium salts decompose or disproportionate. The reaction will proceed to some extent just above the melting point 772 C. of pure potassium fluotitanate and is accelerated with increasing temperature.. However, at temperatures of about 1200 C. or higher excessive decomposition and disproportionation are encountered. Accordingly, a temperature within the range of about 780 to 1150 C. and preferably within the range of about 780 to 1100 C. is useful in the practice of the invention. Within this range temperatures between about 780 to 900 C. result in the formation of trivalent alkali metal titanium fluorides, while temperatures in excess of about 900 C. favor the formation of divalent titanium fluorides.

It is essential that the reaction be carried out in an atmosphere which is inert to the reactants. The presence of even a trace amount of oxygen or moisture in the atmosphere will result in contamination and serious loss in yield of the desired product due to the formation of oxy-fiuorides. Moreover, the reaction is accompanied by the evolution of carbon monoxide from the reaction mixture. Therefore, it has been found advisable to conduct the reaction in an actively pumping vacuum, or in an atmosphere composed of a dry monatomic gas, such as argon, which is continuously cycled through the reaction chamber to withdraw evolved carbon monoxide therefrom.

With the establishment of such an inert atmosphere, the reaction between the oxygen interstitially contained by the titanium metal or titanium base alloy material may be represented by an equation along the following lines:

zTi o aKrriF,

4TiFa.6KF 00 (z-1)Ti 900 o.-115o c. yTi [O] O 2K2TiFs 2TiFa.TiFz.4KF 00 (y-DTi Any suitable inert atmosphere furnace may be used for carrying out the process of my invention. One such furnace construction comprises a steel pot having an open top which can be sealed with a gas-tight lid. Advantageously, the steel pot is internally insulated with a refractory silicious powder held in place against the walls of the pot by means of a graphite liner. An internal heating element is provided, advantageously comprising a graphite resistance element adapted to surround the graphite reaction vessel. The graphite reaction vessel containing the reactants is disposed within the graphite resistance element which, in turn, is centrally positioned in the insulated pot. The necessary electrical connections to the heating element, and the necessary valves and inlet and outlet pipes for the establishment of the inert atmosphere within the furnace, are provided in the gas-tight lid of the steel pot.

To establish an inert atmosphere in the furnace, I presently prefer first to evacuate all of the air from within the furnace, and then to introduce dry argon gas into the furnace, repeating the cycle of evacuation of the atmosphere and replacement with argon gas at least two times. After flushing out the interior of the furnace in this manner, a flow of dry pure argon gas into and out of the furnace is established in order to sweep from the atmosphere in the furnace any carbon monoxide evolved from the reactants in the course of the reaction- The reactants are heated in an inert atmosphere. A furnace such as that described is used to bring the reactants up to a reaction temperature within the range of about 780 to 1150 C. The reactants are held at this reaction temperature for a period of time suflicient to insure that the reaction has gone as close to theoretical completion as the reaction conditions permit. The time required for substantial completion of the reaction depends upon the extent of contamination of the metal, the intimacy of contact between the carbon and the small pieces of contaminated metal, and the temperature of the reactants. A reaction time of from five to ten hours is usually suflicient for the usual amount of oxygen found in commercially available impure titanium sponge or scrap.

On completion of the reaction the fused salt mass is filtered through a porous graphite or carbon filter, thus separating the molten salt from any residual solid materials such as carbon, carbides, titanium metal and oxyfluorides. The purified titanium metal is easily separated from the remaining solids by washing with water or dilute acids. The molten salt filtrate may then be used directly or in admixture with additional diluent alkali metal chlorides in electrolytic processes for the production of titanium metal. The fused salt bath filtration procedure is particularly valuable in the preparation of divalent titanium fluorides, or mixtures of divalent and trivalent titanium fluorides. Divalent titanium fluoride is not generally amenable to aqueous treatment due to the strong reducing properties of divalent titanium salts. Heavy losses in yield can be expected even in highly buffered solutions. Accordingly it is preferable to recover the titannium difluoride containing product in the form of a fused salt bath in which the divalent titanium is present either in simple or complex difluoride compounds.

In an alternative procedure the molten salt filtrate is allowed to cool. The solidified salt cake thus recovered is reddish brown to greyish lavender in color and may contain, besides the lower valent titanium fluorides produced by the reaction, unreduced normal potassium fluotitanate, diluent alkali metal chlorides and any other fusible products that may have formed in the course of the reaction. The lower valent titanium fluoride product can be recovered from the reaction residue by wet chemical treatment.

The recovery of the lower valent titanium product by aqueous procedures is limited in practice to trivalent titanium fluorides. The product salt cake is first crushed to a fine powder and then is leached with cold dilute hydrochloric acid to dissolve the complex potassium salts of lower valent titanium fluorides which are soluble therein, leaving undissolved any potassium fluotitanate or other insolubles. A clear green liquor (characteristic of trivalent titanium solutions) is obtained as the result of the leaching operation, and this liquor is thereupon filtered to remove any insoluble matter. A saturated solution of sodium fluoride is added to the green filtrate while stirring the filtrate until the color changes permanently from green to brownish violet. The solution is then warmed gently (i. e. to a temperature of about 40 to 50 C.), whereupon tannish lavender crystals precipitate out of the solution leaving a violet colored supernatant liquid. The precipitated crystals are recovered by filtering the liquid, and the violet filtrate is again treated with a saturated solution of sodium fluoride. Upon addition of the sodium fluoride solution with stirring, the violet solution gradually becomes substantially colorless, at which point a slight turbidity develops. Gentle warming causes tannish violet colored crystals to precipitate from the solution leaving a water white supernatant liquid. The second batch of precipitated crystals are recovered by filtration and both batches are then washed with distilled water and dried at C.

Although the exact structures of the complex lower valent titanium fluorides are not known with certainty, it has been found that the sodium fluoride derivatives found to contain 25.0% titanium by weight. K TiF contains 19.9% by weight of titanium, the titanium equations is 25.0%

brownish violet.

obtained, as therfirstiand .second preipitates fromrthezg'reemliquor have .completely-ldifierent'rX-rayu pat-terns;

apparentlyniindicative of different fluoride and. potassium, fluoride contents. I However, irrespective: of their precise structure, the lower valent titanium;fiuoride products obtainedv by the practice-of my'invention is free from titanium dioxide, titanium. carbide; potassium; 'fluo-v titanate,-and normal "sodium: and potassium fluorides'and chlorides. These reduced titanium, products are, theref foreavailable for subsequent, use inya highly purej state;

i. .The;titaniurn 'difluorideand vtrifluoride products of the process are useful for a;variety ofgpurposes including: commercially important processes for.;the preparationofi .titanium metal. .,-f

.g 1 l The, following examples areillustrativeybut not limita:

five-pf thepracticegofimy inventionr. v z. 1

'A 'graphitevcrucible was charged with a mixture 'con-' sisting ofi 500 grams of ititanium clippings havingan oxygen'content of 0.28 7 grams' ofi dry recrystallized potassium fluotitanate and ZS' 'grams of '325' mesh (Tyler Standard) lampblack. The crucible wa's heated to a'temperature-of about-850 C. in an inert atmosphere furnace-in which a continuously changing 'a'rgon -atmos phere. had beeri established The-reac'tion mixture was stirred from time to time to'=insu're that the lampblack:

contacted the metal and the fluotitanatethroughout the mixture. The crucible was maintained 'atthe "reaction temperature for 4 hours; The mixture was then filtered through a perforated-graphite plate pierced with a number of fine orifices, while still in an'gargon? atmosphere. Theseparated solids and.,the molten :salt filtrate-were allowed to cool in the furnace. When the temperature had fallen to below 200 C., theargon supply was disconnected and thefurnace was opened. The .separated solids were washed with water and then with alcohol. The purified metal separated cleanly from the carbon lampb lack and other non-moltenbathconstituents jjThe metal product analyzed 0.08% oxygen. Two buttons were prepared by arc melting a sample of the original scrap and of the purified scrap. The Brinell hardness of the two samples were 240 and 150 respectively.

The filtrate was observed to have a reddish color. It was ground to a fine powder. A representative sample of the ground powder was analyzed of titanium and was Since pure content of the salt product represented an increase of 5.1% of the titanium content, over the original content.

ly to the clear green filtrate, while stirring the filtrate,

until the color changed permanently from green to The violet liquor was then warmed to 40 C., whereupon a lavender precipitate settled out. Heating was continued until the temperature of the solution reached 90 C. to keep dissolved and unreacted potassium fluotitanate in solution. The hot aqueous slurry was then filtered to recover the insoluble lavender crystals. To the clear lavender filtrate an additional amount of the saturated solution of sodium fluoride was added until the liquor became nearly colorless and a slight turbidity developed. The solution was again with distilled water and dried at 105 C. fonzfhours. The reducing properties of the-dry--.laven'der ;crystals indicated that lower valent titanium, was present;

It should be pointed. out that both the insoluble residue? from the initial cold hydrochloric acid leaching Lstepf,

and thefinal filtrate from the titanium fluoridei precipitation step contained some unreactedpotassiumfiuotitan ate. This material can be I recovered from the .linsoluble;

residue by hot waterleaching, and; from the leach liquor; and the vfinal filtrate by evaporation and P concentration;

. operations, Thus, unreacted potassiunr'fluotitanate is recoverable' and; can be dried and recycled "throughthe 1 process. After recovery of the unreacted potassiumfluotitanate from the insoluble residue, the remainingt'titanium; content thereof,-made up oftitanium oxides and O fluorides, ,is best recovered by digesting the residuein sulphuric acid. The-resulting sulfate solution is diluted;. filtered to remove free carbon and other insolublesyand is neutralized to precipitate titanium dioxide. v

Example II y A graphitecrucible" was charged with a mixtureof 500 grams titanium plate scrap having an average oxy gen content of 0.28%, 700 grams of dry recrystallized; potassium fluotitanate and ,25 grams of 325 mesh; (Tyler Standard) lampblacki 'The. crucible was heated; to a temperature of about 950 C. in an inert atmosphere furnace in which a continuously changing" argon atn'io's'; phere had been established. The reaction mixturejwas stirred from time to time to insure" that the lampbl lg contacted the metal and the fluotitanate throughout? the' mixture. The crucible Wasmaintained atithereactiodg teniperaturefor 12 hours. The mixture was tli'en'filtered. through a perforated graphite plate pierced with "a' riu m ber of fine orifices, while still in an argon atmosphereQ The separated solids and the' moltenjsalt filtratej'w e allowed to cool invthe furnace. When the'litempe'r hadfallento bel0W200? C,, th'e1 arg'on supply was. connected and the furnace was opened. The separated solids were washed with water and then with alcohol. The purified metal separated cleanly from the carbon lampblack and other non molten bath constituents. The metal product analyzed 0.06 oxygen. Two buttons were prepared by are melting a sample of the original scrap and of the purified scrap. The Brinnell hardness of the two samples was 240 and 140 respectively.

The filtrate was ground to a fine powder after it had solidified and was analyzed for titanium. The salt product was found to contain 27.0% of titanium by weight, which represents an increase of 7.1% over the original titanium content. y

The remainder of the ground salt cake was then mixed with sodium chloride in the ratio of about 5 parts by weight of sodium chloride to 1 part by weight of the salt cake. The resulting mixture was introduced into a suitable vessel and melted therein. When the mixture was molten electrodes were inserted into the melt and an electrolyzing current was initiated between the electrodes. The electrolysis was performed under an inert atmosphere and titanium metal was produced at the cell cathode.

It is apparent from the foregoing description and the examples accompanying same that there has been disclosed a novel and useful process for removingoxygen from oxygen-containing metallic titanium material other than theoxides of titanium, whereby the titanium metal is upgraded to the point that it may be readily fabricated by conventional metal working techniques after it has been reconstituted into the form of an ingot or slab product. In addition, as a by-product of the reaction, there is also contained a lower valent complex alkali metal warmed to 40 C., whereupon a lavender precipitate titanium double fluoride, which isuseful for a variety of purposes including the electrolytic recovery therefrom of metallic titanium.

I- claim: 1

1. The method of removing oxygen from oxygen containing titanium metalwhich comprises bringing together in the presence of carbon a molten alkali metal-titanium double fluoride, in which the titanium is tetravalent and asolid impure titanium metal interstitially containing oxygen at an elevated'temperature within the range of about 780 C. to about 1150 C. under an inert atmosphere, and recovering'from the reaction mixture the solid titanium metal with a diminished oxygen content and separately recovering at least one resulting alkali metaltitanium double fluoride in which the titanium has a valence less than four.

2. The method of removing oxygen from oxygen containing titanium metal which comprises bringing together in the presence of carbon a molten alkali metal-titanium double fluoride, in which the titanium is tetravalent and a solid impure titanium metal interstitially containing oxygen at an elevated temperature within the range of about 780 C. to about 1150 C. under an inert atmosphere, and separating the solid titanium metal with a diminished oxygen content from the reaction mixture.

3. The method of removing oxygen from oxygen containing titanium metal which comprises bringing together a molten alkali metal-titanium double fluoride, in which the titanium is tetravalent and a solid impure titanium metal interstitially containing oxygen in the presence of about 2V2 mols of carbon for each mol of oxygen in the titanium at an elevated temperature within the range of about 780 C. to about 1150 C. under an inert atmosphere, and recovering from the reaction mixture the solid titanium metal with a diminished oxygen content.

I 4. The method of removing oxygen from oxygen containing titanium metal which comprises bringing together in the presence of carbon a molten alkali metal-titanium double fluoride, in which the titanium is tetravalent and a solid impure titanium metal interstitially containing oxygen at an elevated temperature within the range of about 780 C. to about 900 C, under an inert atmos- 8 phere, and recovering from the reaction mixture the solid titanium metal with a diminished oxygen content and separately recovering at least one resulting alkali metalt itanium double fluoride in which the titanium has a valence of three.

5. The method of removing oxygen from oxygen containing titanium metal which comprises bringing together a molten-alkali metal-titanium double fluoride, in which the titanium is tetravalent and a solid impure titanium metal interstitially containing oxygen in the presence of carbon at an elevated temperature within the range of about 900 C. to about 1150 C. under an inert atmosphere, and recovering from the reaction mixture the solid titanium metal with a diminished oxygen content and separately recovering atleast one resulting alkali metaltitanium double fluoride in which the titanium has a valence of two.

6. The method of removing oxygen from oxygen containing titanium metal which comprises bringing together in the presence of carbon a molten alkali metal-titanium double fluoride, in which the titanium is tetravalent and a solid impure titanium metal interstitially containing oxygen, there being. present at least about 2% mols of carbon for each mol of oxygen in the titanium metal at an elevated temperature within the range of about 780 C. to about 1150 C. under an inert atmosphere, and after between 2 and 10 hours at temperature, and separating the solid titanium metal with a diminished oxygen content from the molten reaction mixture. 1

References Cited in the file of this patent UNITED STATES PATENTS 2,707,679 Lilliendahl et a1. May 3, 1955 2,718,464 Gross et al. Sept. 20, 1955 2,723,182 Sibert et al Nov. 8, 1955 2,793,097 McKenna May 21, 1957 FOREIGN PATENTS 723,880 Great Britain Feb. 16, 1955 

2. THE METHOD OF REMOVING OXYGEN FROM OXYGEN CONTAINING TITANIUM METAL WHICH COMPRISES BRINGING TOGETHER IN THE PRESENCE OF CARBON A MOLTEN ALKALI METAL-TITANIUM DOUBLE FLUORIDE, IN WHICH THE TITANIUM IS TETRAVALENT AND A SOLID IMPURE TITANIUM METAL INTERSTITIALLY CONTAINING OXYGEN AT AN ELEVATED TEMPERATURE WITHIN THE RANGE OF ABOUT 780*C. TO ABOUT 1150*C. UNDER AN INERT ATMOSPHERE, AND SEPARATING THE SOLID TITANIUM METAL WITH A DIMINISHED OXYGEN CONTENT FROM THE REACTION MIXTURE. 